It is known that smart cards used in particular as banking cards, such as an identification card, or also as a payment card for different services, are essentially made of a plastic material body of rectangular parallelepiped shape in which is inserted an electronic unit most often made of a semiconductor chip attached to an insulating substrate provided with external electrical contact pads. These external pads enable electrical connection between the circuits in the semiconductor chip and circuits in a read-write device when the card is inserted within such a device.
According to the prevailing standards, the card body should have a thickness of about 0.8 mm. It should be understood that the thickness of the electronic unit is therefore one of its critical parameters, and facilitates the insertion of the electronic unit within the card body and ensures a proper mechanical coupling between the card body and the electronic unit as well as the mechanical integrity of the electronic unit.
In the appended FIG. 1, a vertical cross section of an electronic unit for smart cards made according to a known technique is shown. Electronic unit 10 is essentially comprised of a semiconductor chip 12 in which integrated circuits are formed, this chip having an active face 14 provided with electrical connection terminals 16. The semiconductor chip 12 is attached to an insulating substrate 18 through an adhesive layer 19. The external face 18a of the insulating substrate is provided with external contact pads 20 to be contacted with the electrical contacts of the read-write device. Terminals 16 of chip 12 are connected to external pads 20 through leads such as 24. According to a known method, the
insulating substrate comprises windows 28 with electrical leads 24, so that the use of a doubled-faced printed circuit is avoided. In order to ensure electrical integrity of chip 12 and electrical leads 24, they are encapsulated with an insulating material 26 such as an epoxy resin.
In some cases, the wire leads can be replaced with other electrically conducting elements for connecting the chip terminals to external pads on the insulating substrate.
With such a manufacturing technology, an electronic unit having an overall thickness of about 0.6 mm, is obtained, to be compared with the 0.8 mm thickness of the card body.
Techniques that would allow reducing this thickness are difficult to implement. They could consist in reducing the chip thickness, which is conventionally of the order of 180 μm, but this would unacceptably reduce chip strength. One could also reduce the thickness caused by the curvature of electrical wires 24 or similar electrical connection elements. This, however, requires using the so-called “Wedge bonding” technology which is of costly implementation. Finally, it could be contemplated to reduce the thickness of the insulating resin of encapsulation 26. Such a reduction would however reduce the strength of the electronic unit as a whole.